Pulpstones and method of making



Oct. l1, 1966 A. M. cooK 3,277,611

PULPSTONES AND METHOD OF MAKING Filed April 14, 1964 A TORNEY United States Patent O 3,277,611 PULPSTONES AND METHOD F MAKING Arnold M. Cook, Holden, Mass., assigner to Norton Company, Worcester, Mass., a corporation of Massachusetts Filed Apr. 14, 1964, Ser. No. 359,721 16 Claims. (Cl. 51-206.4)

This application is a continuation-in-part of my application Serial No. 266,302, filed March 19, 1963, and now abandoned.

This invention relates to improvements in pulpstones and to a method of making the same.

Conventionally, as shown in such United States patents as Larsson, 2,141,608, dated December 27, 1938 and Beth, 2,467,878, dated April 19, 1949, a plurality of segmental blocks of abrasive material are fastened in a ring about a rigid core and held bolted thereto by bolts that are prestressed in tension during fabrication of the wheel, so that vin the finished wheel the segmental blocks are held tightly against the peripheral surface in spite of high centrifugal forces developed during high speed rotation of the wheel which tend to pull the segmental blocks away from the surface of the core. Reinforcement of the core itself is provided for by incorporating one or more rows of unstressed hoops in spaced parallel relation widthwise of the core. Hence the only compressive constriction on the core itself is applied by the engirdling segmental blocks.

The principal objects of this invention are to provide an improved pulpstone wherein the facing blocks are held more securely against the surface of the core; and the core, on the one hand, is held in constant compression in spite of centrifugal forces developed in use which may substantially remove the constrictive effect of the facing blocks and, on the other hand, is resistant to destructive compression of the applied work load thereby eliminating the destructive effects of reversal of stresses and hence fatigue. Other objects are to minimize the effect of heating, unequal expansion of the component parts and hence weakening of the bond between parts; and to provide a method of making pulpstones embodying the foregoing characteristics.

As herein illustrated, the pulpstone comprises a rigid cylindrical concrete core to which a plurality of segmental abrasive blocks are secured, collectively to provide -a cylindrical abrasive facing concentric with the core. The segmental blocks are secured to the core by bolts prestressed in tension with their ends anchored, respectively, in the blocks and core and, in accordance with the invention, the inner ends of the bolts are yieldingly anchored to the core. Yielding of the inner ends of the bolts is achieved by pairs of concave sprin-g washers, embedded in the core, through which the ends of the bolts pass and are retained by nuts, which washers yi'eld so as to absorb excess stress without permanent distortion and hence without loss of holding power. In further contrast to current practice, the core is constantly constrictively constrained in compression at operating speed independently of the constrictive effect of the girdling segmental facing blocks and is simultaneously resistant to destructive compression due to applied working pressure. Constrictive compression of the core is obtained by means prestressed in tension and embedded in the core concentrically of the axis of rotation and adjacent the peripheral surfaces. Preferably this means takes the form of a plurality of continuous prestressed hoops disposed in axially spaced parallel relation. Resistance to destructive compression is obtained by a rigid frame disposed inwardly of the constricting hoops comprising concentric rows of unstressed hoops disposed widthwise of the core, the hoops in each row being disposed in spaced parallel relation, spaced parallel rods disposed parallel to the axis 3,27'Zll Patented Oct. ll, 1966 ice of the core and to each other crossing the hoops, and radially disposed rods extending from the inner side of the core outwardly across the hoops, said unstressed hoops, axially extending rods, and radially extending rods being rigidly secured to each other at their places of crossing.

In accordance with one method of making the pulpstone, a plurality of segmental abrasive blocks, 'each having two or more bolts secured thereto, are assembled into a -ring about a central core with a joint-forming mat'erial between the juxtaposed sides of the adjacent blocks and with their bolts projecting inwardly therefrom toward the central core. Reinforcing hoops of smaller diameter than the inside diameter of the abrasive facing ring are now placed within the ring at each side of each row of bolts whereupon a retainer plate, containing -a hole of larger diameter than the bolts, is placed on each bolt with its ends engaged with the inner sides of the reinforcing hoops; a sleeve containing a hole of larger diameter than the bolts is placed on each bolt with its outer end bearing against the retainer plate; a pair of spherically concave spring washers placed with their concave sides adjacent are placed on the inner end of each bolt against the inner end of the sleeve; and a nut is threaded on each bolt against the washers. The nuts are turned up uniformly all around the rows of bolts so as to place the reinforcing hoops and bolts in tension; and, incidentally to place the sleeves and the joint material between the segments in compression. The outer surface of each bolt, nut, spring washer, sleeve, and retainer plate assembly is then coated with a suitable resilient material of sufficient thickness to prevent the concrete from adhering thereto, allows limited movement of each assembly relative to the concrete due to thermal expansion; and prevents heat transfer to the outer peripheral portion of the core. An annular frame is now placed within the space between the inner ends of the bolts and a central core comprised of concentrically disposed, spaced parallel unstressed hoops joined transversely, that is, widthwise of the stone by spaced parallel rods parallel to each other and to the axis of the stone and radially by radially extending rods extending from the central core outwardly across the hoops and terminating at their outer ends adjacent the constricting hoops. Having assembled the foregoing parts around the central core, a suitable mixture of concrete is poured into the structure between the circle of blocks and the central core. By successively building one ring o'f segments upon another, a stone of any desired axial length may be fabricated.

The invention will now be described in greater detail with reference to the accompanying drawings wherein:

FIG. 1 is a diametrical fragmentary section of an yarcuate portion of a pulpstone showing a plurality of peripherally disposed segmental blocks and the improved attaching and reinforcing means which forms the subject matter of this invention.

FIG. 2 is a transverse section taken widthwise of the stone on the line 2--12 of FIG. 1; and

FIG. 3 is a plan view, partly broken away, showing a portion of a surface of one block and the relation of the prestressed reinforcing hoops to the .attaching Ibolts holding the segments on the peripheral surface of the core.

Referring to the drawings, the pulpstone is comprised of a plurality of segmental-shaped blocks 10 of suitable abrasive material supported on the peripheral surface of a cylindrical core 1-2, having a central opening 14 by means of which the pulpstone may be mounted on a suitable lspindle or hub for rotation. As illustrated, each of the blocks 10 is secured to the core 12 by four bolts 16, the outer ends 18 of which are provided with Ia coarse thread 20 or a plurality of axially spaced ribs adapted for a-nchorage in radially disposed holes 22 in the blocks in the same fashion as disclose-d in United States Patent 2,421,- 885 to Howe, issued June 10, 1947. The inner ends of the bolts 16 are threaded at 24 and extend through pairs of .spherically concave washers 26 placed with their ooncave surfaces adjacent each other and embedded in the core. As will appear more fully below, when nuts 28 are screwed onto the threaded ends of the bolts against the inner ones of the Washers, the bolts are held stressed in tension between the segmental blocks and the washers which in turn are supported by the reinforcing means within the core and during fabrication the thread end of the bolts 16, washers 26 and nuts 28 are coated with latex or a like resilient material 25 of sufficient thickness which prevents adhesion of the parts to the concrete of the core; yet allows limited movement relative to the concrete due to thermal expansion of the bolts, .and substantially good transfer of heat from the ends of the bolts to the concrete core nearer the center of the stone. The spring washers yieldingly hold the segmental blocks against the exterior surface of the core and simultaneously resists centrifugal forces developed in the rotating stone which tend to separate the segmental blocks from the surface of the core. The Washers are comprised of spring steel so that they are able to vabsorb excessive pressure without permanent distortion while allowing for limited movement without loss of resilience, and hence without loss of holding power.

Metal reinforcing hoops 30 are embedded in the core, one at each side of each row of bolts as shown in FIG. 2. The reinforcing `hoops 30 .are located close to the surface of the core and are prest-ressed in tension as the concrete is poured around them, which tension is subsequently ltransferred so that rings 30, then apply continuous uninterrupted constrictive pressure to the core inwardly thereof, which is independent of the constrictive forces exerted by the segmental blocks. As .an incident of fabrication, a sleeve 34 is disposed about each bolt with the inner en-d of the sleeve bearing against the outer one of lthe washers 26 and the outer end of the sleeve bearing against a retainer plate 36 containing a hole of larger diameter lthan the bolt, positioned around the bolt with the periphery of the plate bea-ring against the inner sides -of the reinforcing hoops 30. The sleeves are of larger inside diameter than the bolts so that the latter pass freely through them. When the wheel is'in use it is heated and the larger holes eliminate direct contact between the bolt which is heated by contact with the peripheral segments, and the sleeve land plate to minimize the flow of heat from the plates and sleeves to the surrounding concrete. The inner end of the bolt is in more direct contact with the core and most of the heat iiow from the bolt arrangement, is between the end of the bolt to the inner phase of the core so that heat is more uniformly distributed through the mass of the wheel. In addition the plates, sleeves, and upper portion-s of the bolts are coated with latex of like resilient material 37 during fabrication of the stone which prevents vadhesion t-o the concrete; yet allows limited movement due to ther-mal expansion, and tends to insulate heat from being transferred to the concrete that embeds them.

It is preferable to transfer the greater part of the heat generated to the center of the core where it will -be distributed uniformly and produce la gradual and uniform expansion of the core during starting up of the wheel and more rapid and uniform distribution of heat when conditions change during use.

A rigid annular frame is embedded in the core inwardly of the inner ends of the bolts 16 and provides rigid resistance to destructive comprrsion and crushing of the core unde-r forces applied by the work. The frame is made up of concentric rows of unstressed hoops 38 and 40 concentric to the axis of the core and arranged in spaced parallel relation widthwise of the core, the hoops 38 being of larger diameter and located adjacent the inner ends of the bolts 16 an-d the hoops 40 being of smaller diameter and located near `the central opening 14 at the center of the core. The hoops 38 are joined widthwise of the core to form a rigid cylindrical cage by spaced parallel, .straight rigid rods 42 arranged at substantially uniform intervals peripherally thereof in contact with their inner sides and are welded thereto where they cross. The hoops 40 .are similarly joined widthwise of the core to form a rigid cylindrical cage by straight rigid rods 44 welded to their inner sides. The two cages are joined to each other by a plurality of stirrups 46, each of which comprises a straight length of rod 4S and integral divergent lengths of rod 50-50 at its opposite ends, the straight and divergent lengths .of rod lying in planes at right angles to the axis of the cofre. The stirrups are spaced about the axis of the core so that the radial lengths of rod 50 `are situated at substantially equal angular distances from each other about the axis. The stirrups 46 are disposed adjacent the hoops 3S land 40 and about the rods 42 and 44, so that the straight lengths of rod 48 extend across a pair of adjacent rods 44-44 and the divergent portions 50-'50 extend substantially radially outward from the opening 14 across the hoops 42 and 44 and terminate adjacent the inner sides of the hoops 30 Abetween adjacent rows of bolts. The rod-s 48 and 50 are welded or otherwise suitably fastened at their points of crossing to the hoops 38 .and 40 and to the rods 42 and 44.

As will be described in more detail below, the structure is assembled with the blocks 10 arranged in a cylindrical pattern with their edges in abutting relation and bolts 16 tensioned to hold the entire assembly tensioned against rings 30. The concrete core 12 is then poured to fill the space provided within the blocks 10 and the form for the central opening 14. After the concrete has hardened, the wheel is put into use and the tension of the bolts 16 hol-ds the .blocks against the surface of the core. In the meantime the abutting pressure between the edges of the `blocks is relieved so that the keystone effect between the blocks used to tranmsit tension to rings 30 is relieved and the tension in rings 30 now is all applied as a prestressed compression force applied near the periphery of the core 12.

As thus constructed, the initial tension in the bolts 16 has now been transformed to a direct force from the blocks 10 through bolts 16 and their associated structure to constrain the segmental blocks against the peripheral surface of the core. The inital prestress in rings 30 has now been transferred to apply compression to the core. The rings 30 and tensioned :bolts 16 continue to cooperate however to resist separation of the blocks from the periphery of the core due to centrifugal forces developed by high speed rotation. The spring washers supplement the prestressing in the bolts and insure holding the 'blocks onto the periphery of the c-ore even though the bolts may be slightly stretched, since they will recover in spite of distortion. Pull applied to the bolts is thus cushioned by the washers without adding tension in the hoops 30 and hence wit-hout lessening their effectiveness in holding the core under constrictive compression. The prestressed hoops 30 thus apply constrictive pressure to the core unaiected by the centrifugal forces developed in the facing blocks.

The reinforcing frame, situated inwardly of the constricting hoops 30 and the bolts 16 as previously mentioned, is comprised of unstressed hoops and rods which reinforce the core against excessive compression and bending due to the application of the work load.

A wheel is thus provided with a maximum resistance of the facing to loosening and maximum resistance of the core, on the one hand, to destructive forces of centrifugal action and, on the other hand, to destructive compression by the work load. The constrictive hoops, in combination with the reinforcing frame, substantially eliminate reversal of stresses in the core during use and ,hence the destructive effect of fatigue.

The relatively long metal bolts have substantially no direct contact with the outer part of the core, because of the fact that the bolts, plates, and sleeves are coated with latex of suicient thickness during fabrication to insulate heat therefrom; hence, heat developed in the facing of the wheel during the start up and in use is transmitted directly through the length of the bolts, into the heart of the core. Dispersion of the heat throughout the inner phases of the core .relatively uniformly eliminates unequal expansion of the component parts and any tendency for them to pull apart.

The stone is fabricated in conventional fashion as disclosed in the aforesaid Howe Patent 2,421,885, by `assembling the segmental blocks with spacers 52 between their abutting edges, to form a ring and with the bolts 16 secured to their inner sides so as to project inwardly therefrom to form a central core. The bolts are fastened to the blocks, as disclosed in the aforesaid Howe patent, and the blocks, in turn, are temporarily held in place, for example, by holding members such as circular clamps (not shown). The reinforcing hoops 30 are now placed within the ring of segmental blocks at opposite sides of the rows of bolts, the hoops being supported in known fashion to hold them in position. The retainer plates 36 are now mounted on the bolts and moved radially outwardly into engagement with the inner sides of the yhoops 30 whereupon the sleeves 34 are mounted on the bolts with their outer ends engaged with the retainer plates, the Washers 26 are placed over the inner ends of the bolts against the ends of the inner ends of the sleeve, and the nuts 28 are applied to the threaded ends of the bolts. The nuts are turned up tightly enough to impart a tension of approximately 2500 pounds to each of the bolts which is transmitted through the sleeves and retainer plates to the hoops 30 so as to stress the latter in tension. At this point in the fabrication of the stone the bolts 16 are under tension, the sleeves 34 are under compression and the hoops 30 are under tension.

The outer surfaces of the bolts 16, nuts 24, washers 26, sleeves 34 and retainer plates 36 are then coated with latex 37 or an equivalent substance having plastic flow characteristics as described above.

The joint-forming material 52 which is employed, is stable during assembly of the component parts, that is, will withstand prestressing of the parts created by t-he keystone disposition of each segment prior to and during curing of the concrete cores. A thermoplastic joint ller such as disclosed in the Larsson Patent 2,054,771, dated September 15, 193 6, is suitable.

An end of the annular frame 46 is now disposed within the circular assembly of abrasive segments between it and the central core with the radially extending ends of the lengths of rods 50 located within the ring, situated between subjacent rows of bolts. A mixture of core-forming material, for example ordinary concrete, is poured into the space between the ring of blocks and the core so as to completely embed the assembly hoops, bolts, fastening means and the portion of the reinforcing frame within the circle of abrasive segments. The stone is built up to the desired axial length by placing successive assemblies over the frame and filling the entire center core concrete at one time. The cylinder is allowed to cure under controlled moisture conditions to minimize shinkage.

Following curing, the stone is put into use and gradually heats up to a working temperature. As the heat ows into the stone, the entire structure expands and simultaneously the bolts 16 elongate as they become heated. The core heats slowly and uniformly because the body of each of the lbolts is somewhat insulated from the core and the bolts are purposely made long enough to deliver a substantial amount of the heat from their inner ends into the internal phases of the mass of concrete to assure a more even distribution of heat.

When the wheel is heated the whole mass expands under the influence of heat and the initial compression between the adjacent edge surfaces of the segments is relieved as the material 52 of the spacers gives way so that each segment now exerts pressure solely against the outer surface of the core by the tension in the bolts 16. Since there are four of these bolts in each .segment in the preferred form of my invention, the segments are held tightly against the periphery of the core u-nder about 10,000 pounds pressure. The tension of the bolts which was resisted by keystone construction of the ring of segments is now transferred directly to each block individually to hold them tight against the surface of the core simultaneously relieving the hoops 30 of the initial tension produced by the keystone arrangement allow the initial prestressing in tension of the hoops 30 to now be applied -to the core within the hoops independently of the edgewise pressures exerted by the segmental blocks.

The bolts 16 act through the spring washers 26, sleeves 34 and plates 36, all of which may have limited movement relative to the core under the influence of heat due to the plastic flowability of the non-adhering latex or other resilient coating positioned between them and the core. The spring washers 26 serve to hold the segments tightly against the surface of the core in spite of expansion of the bolts as -the temperature is raised.

The aforesaid construction and, in particular, the reinforcing frame 46 is extremely useful in wide stones the frame 46 serving to support the center of the stone against undue deection. In the event that the periphery of the stone is loaded in use, in a manner which tends to deflect the sur-face inwardly, the bars 44 are subjected to tensile loading and their resistance to such loading counteracts the deflecting load applied to the surface. The hoops 38 and 40 and the rods 42 serve to take up this load and distribute it evenly throughout the mass of the core.

It should be understood that the present disclosure is for the purpose of illustration only `and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

I claim:

1. A pulpstone comprising a core having a circular cross-section and a plurality of segmental blocks disposed .about the peripheral sur-face of the core collectively forming a cylindrical -abrasive facing, means securing the blocks to the core in compressive contact with the peripheral surface, and circumferentially continuous means stressed in tension disposed in the core, adjacent the peripheral surface concentric with the axis of rotation of the core, for constrictively compressing the core independently of 4the compressive forces imparted thereto by the segmental facing blocks.

2. A pulpstone comprising a large mass of a reinforced concrete forming a core, a plurality of segmental blocks disposed about the core; radially disposed bolts having an elongated body secured at their ends to the blocks and to the core respectively, said bolts being placed under tension for holding the blocks in compressive engagement with the peripheral surface of the core, said blocks collectively forming a cylindrical abrasive facing girdling the core, and a heat insulating means between the elongated body of each of the bolts and the core whereby heat generated by the -action of the pulpstone in use is dissipated deeply into the body o-f the core by being trans` ferred along the elongated bodies of the bolts.

3. A pulpstone comp-rising a core having a circular cross-section disposed about an axis of rotation, a plurality of segmental blocks disposed about the peripheral surface of the core collectively forming a cylindrical abrasive facing, continuous metal hoops embedded in the core in axially spaced parallel relation concentric with the axis of rotation, said hoops being stressed in tension for constrictively compressing the core within them, rows of vbolts in tensi-on disposed radially in the core between adjacent hoops, said bolts having inner and outer ends and being secured at their outer ends .to the blocks, said bolts serving to hold the blocks against .the peripheral surface of the core whereby to constrictively hold the portion of the core in contact with the blocks and externally of the hoops in compression, and means disposed in the core about the bolts, said last named means being constrained in compression between the hoops at their outer ends and the inner ends of the bolts in the core.

4. A pulpstone comprising a cylindrical core having an axis about which it rotates, a plurality of segmental blocks disposed about :the peripheral surface of the core collectively forming a cylindrical abrasive facing, circumferentially continuous metal hoops embedded in the core adjacent the periphery of the core and disposed in spaced parallel relation concentric with the axis of rotation, said hoops being stressed in tension for constrictively compressing the core material contained within them, rows of radially disposed bolts having inner and outer ends, the bolts being situated between adjacent hoops, said bolts being under tension and secured at their outer ends to the blocks, -anchoring means for the bolts embedded in the core, the portion of the bolts between said ends being free from attachment t-o Ithe core and said bolts being operable to hold the blocks engaged with the peripheral surface of the core, and resilient means disposed in the core for cooperation with the bolts, said last named means being constrained in compression between `the hoops and the inner ends of the bolts to produce tension in the bolts.

5. A pulpstone according to claim 4, wherein the resilient means includes; pairs of concave spring washers, disposed with their concave sides facing, through which the inner ends of the bolts pass, and nuts on :the bolts securing the washers compressed between the hoops and the ends of the bolts.

6. A pulpstone comprising a icore having a circular cross-section, a plurality of segmental blocks disposed about the peripheral surface of the core collectively forming a cylindrical abrasive facing, circumferentially continuous metal hoops embedded in the core adjacent the surface in spaced parallel relation concentric inside the periphery of the core, said hoops being stressed in tension, rows of bolts stressed in tension disposed between adjacent hoops, said bolts being secured at their outer ends to the blocks, pairs of concave spring washers embedded in the core secured by nuts to the inner ends of the bolts, bearing plates embedded in the core with their ends engaged with t-he inner sides of the hoops, said bearing plates containing holes of larger diameter than the bolts through which the bolts pass, and rigid sleeves disposed about the bolts in compression with their ends, respective- 1y, engaged with the bearing plates and the washers.

7. A pulpstone as in claim 6 wherein the exposed surface of said bolts, plates, sleeves and washers are coated with `a thin layer of non-adhering resilient material prior to being embedded in the core.

8. A pulpstone comprising a core having a circular cross-section, and a plurality of segmental blocks disposed about the outer surface of the core collectively forming a cylindrical abrasive facing, means securing the blocks to the core for compressive contact with said surface, circumferentially continuous means stressed in tension disposed in the core adjacent the surface for constrictively constraining the core independently of the compressive force imparted thereto by the facing blocks, and reinforcing means embedded in the core inwardly of the continuous means resistant to destructive compression, said embedded means including a plurality of concentrically disposed hoops, axially disposed rods secured to the hoops at peripherally spaced intervals, and radially disposed rods secured to the hoops and said axially disposed rods at their places of intersection.

9. A pulpstone comprising a core having a circular cross-section, a plurality of segmental blocks secured across the width of the core in constrictive engagement with the peripheral surface thereof, hoops stressed in tension embedded in the core adjacent the surface for constrictive constraining the core, and a compressive resistant structure embedded in the core inwardly of the prestressed hoops, said structure including spaced parallel unstressed hoops, spaced rods axially disposed widthwise of the core, and radially disposed rods disposed at spaced intervals widthwise of the core; said axially disposed rods and radially disposed rods crossing the unstressed hoops and each other; said crossed rods and hoops being rigidly joined together at the places of crosslng.

16. A pulpstone comprising a cylindrical core, a plurality of segmental blocks disposed about and engaging the core collectively forming a cylindrical abrasive facing, bolts radially situated in the core, said bolts being stressed in tension and secured at their outer ends, respectively, to the segmental blocks and to means in the core for holding the blocks in compressive engagement with the peripheral surface of the core, hoops stressed inrtension embedded in the core adjacent the peripheral surface for constrictively embracing the core, and concentric rows of unstressed hoops embedded in the core widthwise thereof, the unstressed hoops in each row being disposed in spaced parallel relation, a plurality of rods disposed widthwise of the core parallel to its axis in uniformly spaced relation in contact with hoops of the two rows of unstressed hoops, and radially extending rods extending through the core across the unstressed hoops of the two rows in contact with said hoops and the other rods, the outer ends of the radial rods terminating between the bolts adjacent the inner sides of the first mentioned stressed hoops, means joining the inner ends of the radial rods, andsaid unstressed hoops, radially extending rods and the other rods being rigidly joined at their places of contact.

11. A pulpstone comprising la cylindrical core, a plurality of segmental blocks disposed about and engaging the core collectively forming a cylindrical Iabrasive facing, bolts stressed in tension secured at their ends, respectively, to the blocks and core for holding the blocks in compressive engagement with the peripheral surface of the core, metal hoops stressed in tension embedded in the core adjacent the peripheral surface constrictively embracing the core within them, concentric rows of unstressed metal hoops disposed widthwise of the core, the unstressed hoops in each row being disposed in spaced parallel relation, the unstressed hoops in one row being of smaller diameter than those in the other row, a plurality of spaced rods disposed widthwise of the core parallel to the axis of the core, said rods being disposed at equal intervals around the unstressed hoops and being in contact with the inner sides of the unstressed hoops, and stirrup members including divergent radially disposed rods with ties joining their closed ends, said stirrups being disposed to be in contact with the inner and outer unstressed hoops, and said unstressed hoops, rods and stirrups being rigidly joined to each other at their points of contact.

12. A pulpstone comprising a core, a plurality of segmental blocks disposed about and engaging the core, and means for constrictively holding the segmental Iblocks engaged with the peripheral surface of the core, comprising bolts stressed in tension, one4 end of each of said bolts being secured to the blocks and the other end movably carried in the core, means for supporting the bolts relatively xed in the core, pairs of concave spring washers embedded face-to-face in the core through which the inner ends of the bolts pass and means to compress the washers on the bolts between the free end of the bolt and said support means whereby to produce the tension stress in the bolts to hold the blocks on the surface of said core.

13. The method of making a pulpstone comprising forming a circle of segmental blocks with a temporary joint-forming material between the adjacent sides and ends of the blocks, said blocks being assembled to collectively provide a cylindrical grinding face, securing the ends of at least two bolts to the inner side of each block so that the bolts extend radially inwardly therefrom toward the center of the circle, supporting at least one reinforcing hoop of smaller diameter than the inside diameter of the circle of blocks adjacent each row of bolts, mounting a retainer plate containing a hole of larger diameter than the bolt on each bolt with the plate bridging and engaging the inner side of the reinforcing hoops, mounting a sleeve containing a longitudinal passage of larger diameter than the bolt on each bolt with one end of the sleeve bearing against the retainer plate, securing spring washers to the inner end of each bolt against the inner end of the sleeve by means of a nut threaded onto the bolt, tightening the nuts to impart suicient tension to the bolts to produce -a keystone effect in the blocks and place the reinforcing hoops adjacent each row of bolts in tension and the sleeves in compression, casting a hardenable mix into the interior of the circle of blocks to form a rigid core within which the stressed components are embedded, and the removing the temporary joint forming material from between the blocks to release the tensile stress produced in the hoop to exert a compressive force on the rigid core..

14. A method of making a pulpstone comprising assembling a plurality of segmental blocks having parallel sides and radially shaped ends into a ring with a temporary joint filler between the radial faces thereof, assembling a plurality of rings to form a cylindrical grinding facing made up of blocks disposed both axially and in circular rows, fixing the outer ends of a plurality of bolts to the blocks so that the bolts extend radially inwardly toward the center of the cylinder, said bolts being disposed in alignment to form rows, placing reinforcing hoops in symmetrically spaced relation to each row of bolts, mounting a retainer plate containing a hole larger than the bolts on each bolt with the plate bearing on the hoops at sides of each row of bolts, placing a sleeve containing a hole which is of larger diameter than the bolt on each bolt with its outer end bearing against the retainer plate, applying pairs of concave spring washers and nuts to the inner ends of the bolts to produce :a tension in each bolt in the order of at least 2000 pounds tensile pull to produce a tensile stress in the reinforcing hoops and to compress the sleeves, coating the exposed surface of the bolts, nuts, plates, washers and sleeves with a substance having plastic flow characteristics, casting a hardenable mixture into the interior of the cylinder to form a rigid core, and then removing the temporary joint ller.

15. A pulpstone comprising a core having a generally circular cross-section and a plurality of segmental blocks secured about and in contact with the peripheral surface of the core, said blocks collectively forming an abrasive facing around the core, means securing the blocks to the core in compressive contact with the peripheral surface and separate reinforcing means stressed in tension disposed in the core for constrictively compressing the core inwardly from its peripheral portion independently of the compressive forces imparted thereto by the segmental facing blocks.

16. A pulpstone according to claim 1S having in addition an internal unstressed reinforcement frame means to provide resistance to destructive compressive forces applied to the surface of the pulpstone in -a direction to produce `bending stresses therein.

References Cited by the Examiner UNITED STATES PATENTS Re. 19,678 10/1935 Benner et al. 51--206.5 699,302 5/ 1902 Fowler et al. 51-206.6 1,865,523 7/1932 Ieppson et al. 51--206.5 2,177,550 10/1939 Patt 51-206.5 2,279,486 4/ 1942 Patt 51-206.5 2,516,693 7/ 1950 Frost 51-206.4

ROBERT C. RIORDON, Primary Examiner.

LESTER M. SWINGLE, Examiner. L. S. SELMAN, Assistant Examiner, 

15. A PULPSTONE COMPRISING A CORE HAVING A GENERALLY CIRCULAR CROSS-SECTION AND A PLURALITY OF SEGMENTAL BLOCKS SECURED ABOUT AND IN CONTACT WITH THE PERIPHERAL SURFACE OF THE CORE, SAID BLOCKS COLLECTIVELY FORMING AN ABRASIVE FACING AROUND THE CORE, MEANS SECURING THE BLOCKS TO THE CORE IN COMPRESSIVE CONTACT WITH THE PERIPHERAL SURFACE AND SEPARATE REINFORCING MEANS STRESSED IN TENSION DISPOSED IN THE CORE FOR CONSTRICTIVELY COMPRESSING THE CORE 